Since the early 1970s, when optical data storage and recording first became practical, a large number of patents has issued describing such media. Generally, optical data storage and recording media may be typified as either reflective or absorptive in nature. Reflective media have a reflective surface whose reflectivity is altered to encode data. Absorptive media has an opaque absorptive surface whose opacity is altered to encode data. There is one particular type of media that permits instant laser recording without processing. It is sometimes referred to as direct-read-after-write, or DRAW, media.
U.S. Pat. No. 3,889,272, issued June 10, 1975, to Lou and Willens of Bell Telephone Laboratories describes the use of a thin metal film and an anti-reflection layer to make a reflective optical data recording medium. The thin continuous conductive metal layer is partially melted by laser pulses, thereby encoding data. The anti-reflection layer is disposed atop the metal film and is composed of metal crystallites.
U.S. Pat. No. 3,911,444, issued Oct. 7, 1975, to Lou, Watson and Willens of Bell Telephone Laboratories describes the use of a relective metal film disposed atop a plastic film. Again, the metal film used in this patent, as with all of the other metal films mentioned in this prior art section, is a continuous and electrically conductive film, usually deposited by vacuum sputtering or evaporation.
U.S. Pat. No. 3,971,874, issued July 27, 1976, to Ohta and Takenaga of Matsushita Electric Industrial Company describes the use of a thin reflective film of tellurium oxide. Tellurium oxide is vacuum deposited onto a transparent base. Initially, the tellurium oxide is brown in color, and laser recording is possible by either heating the tellurium oxide so that it changes color or by melting the tellurium oxide and thereby forming a hole.
U.S. Pat. No. 3,990,084, issued Nov. 2, 1976, to Hamisch and Kaiser of Robert Bosch Company describes the use of a thin reflective metal film of bismuth and selenium to form a thin metal film for laser recording.
U.S. Pat. No. 4,000,492, issued Dec. 28, 1976, to Willens of Bell Telephone Laboratories describes a recording medium comprising a reflective radiation absorbing metal film disposed on a transparent substrate. The novel aspect of this patent is the reduction in laser energy required to create holes in the metal film by the introduction of an anti-reflection layer between the thin metal film and the incident radiation. The purpose of the anti-reflection layer is to substantially increase the amount of energy absorbed from incident laser radiation. The anti-reflection layer consists of BiS.sub.3, SbS.sub.3, or Se.
RCA has announced a trilayer system which consists of a dark, absorptive surface layer; a transparent layer; and a thin, continuous metal layer. A laser burns through the absorptive layer to record data which will be read as a reflective spot in a dark field.
Eastman Kodak Company has recently disclosed a solvent coatable reflective optical data storage medium which consists of a dye filled layer disposed atop a thin, reflective, continuous metal layer. A recording laser beam is absorbed by the dyed layer, melting it. The dyed layer is transparent to the reading laser, allowing the data to be read as differential phase shifts.
All of the above mentioned prior art discloses the use of a continuous electrically conducting thin metal film to form a reflective optical data storage and recording medium.
U.S. Pat. No. 4,176,277, issued Nov. 27, 1979, to Bricot, et al. of Thomson-Brandt describes the use of a thin metal film disposed atop a thermally deformable plastic. When a small localized area of the thin metal film is heated to a high temperature, for example by a laser, the thermally deformable plastic immediately below the heated area of the metal film deforms thereby encoding data.
U.S. Pat. No. 4,188,214, issued Feb. 12, 1980, to Kido, et al. of Fuji Photo Film Company describes the use of a thin metal film combined with one or more metal sulfides. The addition of metal sulfides increases the absorptivity of the thin metal film to incident recording radiation.
U.S. patent application Ser. No. 55,270, filed July 6, 1979, now U.S. Pat. No. 4,278,756, by Bouldin and Drexler of Drexler Technology Corporation, describes a method of making reflective, electrically non-conductive, silver optical data storage and recording materials. A fine grained silver-halide emulsion photosensitive material has latent images created in it, and subsequently the silver halide is subjected to solution physical development. This solution physical development creates reflective non-filamentary silver particles which form the reflective recording and data storage surface. This is a direct-read-after-write media.
Accordingly, it is an object of the present invention to achieve a more sensitive and versatile reflective optical data storage and recording medium. Another object of the present invention is to create a reflective optical data storage and recording medium using reflective read methods over a wavelength range of 440 nanometers to 830 nanometers, those wavelengths being the most common wavelengths for laser sources in the visible and near-infrared.